Journal of Vacuum Science & Technology A publishes reports of original research, letters, and review articles that focus on fundamental scientific understanding of interfaces, surfaces, plasmas and thin films and on using this understanding to advance the state-of-the-art in various technological applications.

A multistage coevaporation process for the direct growth of Cu2ZnSnS4 (CZTS) thin films without additional atmospheric sulfurization was investigated. To obtain reproducible CZTS films, in situ process monitoring of the film growth was developed by measuring the apparent substrate temperature (Tpyro) using a pyrometer. After CZTS depositions terminated at various endpoints, ex situ characterization of the film properties was performed to clarify the growth mechanism of the films. The results provided clear evidence that CZTS phase formation was significantly delayed via re-evaporation of Sn–S-based compounds in the early part of the first stage, leading to the initial formation of a dominant (CuS + ZnS) structure that coexisted with a small amount of CZTS. CZTS phase formation was then facilitated by the (CuS + ZnS) precursor via a Cu-rich to Cu-poor sequence with an apparent variation in Tpyro during the second stage, and the slightly segregated CuS phase was nearly consumed under (Zn + Sn + S) fluxes. Consequently, CZTS thin films containing close-packed grains with a single kesterite structure were successfully grown under excess Sn and S fluxes, even at moderate Tsub below 500 °C. The best solar cell with a Glass/Mo/CZTS[Cu/(Zn + Sn) = 0.71, Zn/Sn = 1.6]/CdS/ZnO:Ga structure and a NaF precursor layer yielded an active area (0.170 cm2) efficiency of 3.84% (Voc = 567 mV, Jsc = 11.3 mA/cm2, and FF = 0.603). The diode properties under dark and light conditions were also evaluated.

Oxygenated cadmium sulfide (CdS:O) is commonly used as the n-type window layer in high-performance CdTe heterojunction solar cells. This layer is deposited by reactive sputtering, but the optimal amount of oxygen in the sputtering ambient is highly dependent on the specific system and process employed. In this work, the intrinsic properties of CdS:O were measured as a function of the oxygen content (0%–10%) in the sputtering ambient and correlated to device performance with the goal of better defining optimal CdS:O properties for CdTesolar cells. Optimal performance was found using CdS:O films that contained ∼40 at. % oxygen as measured by Rutherford backscattering spectrometry. X-ray photoelectron spectroscopy confirmed these results and showed that oxygen is incorporated primarily as oxygenated sulfur compounds (SOx). Device efficiency improved from 10.5% using CdS to >14% with CdS:O due largely to increases in short-circuit current density as well as a modest improvement in open-circuit voltage. The transparency of the CdS:O films was well correlated with observed improvements in blue quantum efficiency with increasing oxygen content. The optical bandgap of as-deposited CdS:O was identified as a simple metric for process optimization and transfer, with 2.8 eV being ideal for the device architecture employed.

A new process has been developed to deposit magnesium fluoride (MgF2) thin films via atomic layer deposition(ALD) for use as optical coatings in the ultraviolet. MgF2 was deposited in a showerhead style ALD reactor using bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride (HF) as precursors at substrate temperatures from 100 to 250 °C. The use of HF was observed to result in improved morphology and reduced impurity content compared to other reported MgF2ALD approaches that use metal fluoride precursors as the fluorine-containing chemistry. Characterization of these films has been performed using spectroscopic ellipsometry, atomic force microscopy, and x-ray photoelectron spectroscopy for material deposited on silicon substrates. Films at all substrate temperatures were transparent at wavelengths down to 190 nm and the low deposition temperature combined with low surface roughness makes these coatings good candidates for a variety of optical applications in the far ultraviolet.

Atomic layer deposition(ALD) holds markedly high potential of becoming the enabling method for achieving the three-dimensional all-solid-state thin-film lithium ion battery (LiB). One of the most crucial components in such a battery is the electrolyte that needs to hold both low electronic conductivity and at least fair lithium ion conductivity being at the same time pinhole free. To obtain these desired properties in an electrolyte film, one necessarily has to have a good control over the elemental composition of the deposited material. The present study reports on the properties of ALDlithiumaluminum oxide (LixAlyOz) thin films. In addition to LiB electrolyte applications, LixAlyOz is also a candidate low dielectric constant (low-k) etch stop and diffusion barrier material in nanoelectronics applications. The LixAlyOz films were deposited employing trimethylaluminum-O3 and lithiumtert-butoxide-H2O for Al2O3 and Li2O/LiOH, respectively. The composition was aimed to be controlled by varying the pulsing ratio of those two binary oxide ALD cycles. The films were characterized by several methods for composition, crystallinity and phase, electrical properties, hardness, porosity, and chemical environment. Regardless of the applied pulsing ratio of Al2O3 and Li2O/LiOH, all the studied ALD LixAlyOz films of 200 and 400 nm in thickness were polycrystalline in the orthorhombic β-LiAlO2 phase and also very similar to each other with respect to composition and other studied properties. The results are discussed in the context of both fundamental ALD chemistry and applicability of the films as thin-film LiB electrolytes and low-k etch stop and diffusion barriers.

The authors report on highly flexible and transparent Agnanowire (NW) coated graphene hybrid electrodes for flexible organic solar cells (FOSCs). Brush painted Ag NW percolating network on the transparent graphene sheet led to an invisible Ag NW/graphene hybrid electrode with a sheet resistance of 15.25 Ω/sq. and a high optical transmittance of 77.4% as well as superior flexibility. In particular, similar bending radius of Ag NW/graphene hybrid electrode to graphene bilayer electrode during outer bending test demonstrated the superior mechanical flexibility of the Ag NW/graphene hybrid electrodes. FOSCs fabricated on Ag NW/graphene hybrid electrode showed higher power conversion efficiency (2.681%) than that (1.681%) of FOSC with graphene bilayer electrode due to lower sheet resistance and improved wettability for hole extracting layer. This indicates that brush painting of conductiveAg NW is a critical solution to solve the problem of high resistance and hydrophobic grapheneelectrode for use in FOSC.

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The authors investigated the etchingcharacteristics and mechanisms of (In, Ga, Zn)O (IGZO) thin films in CF4/Ar/O2inductively coupled plasmas. The etching rates of IGZO as well as the IGZO/SiO2 and IGZO/Al2O3etching selectivities were measured as functions of O2 content in a feed gas (0%–50%) and gas pressure ( = 4–10 mTorr) at fixed input power ( = 700 W) and bias power ( = 200 W). It was found that the IGZO etching rate decreases monotonically toward O2 rich plasma but exhibits a maximum under gas pressure conditions. The zero-dimensional plasma model with Langmuir probe diagnostics data provided the information on plasma parameters and densities of plasma active species. The model-based analysis shows the dominance of the ion-flux-limited etching regime at ≥ 6 mTorr as well as the noticeable influence of CFx radicals on the overall etching kinetics.

This paper reports the effect of helium gas pressure upon the structural, nanomechanical, and photoconductive properties of nanocrystalline carbon thin (NCT) filmsdeposited by the filtered cathodic jet carbon arc technique. High-resolution transmission electron microscopy images confirm the nanocrystalline nature of the depositedfilms with different crystallite sizes (3–7 nm). The chemical structure of the depositedfilms is further analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy, which suggest that the depositedfilms change from graphitelike to diamondlike, increasing in sp3 content, with a minor change in the dilution of the inert gas (helium). The graphitic character is regained upon higher dilution of the helium gas, whereupon the films exhibit an increase in sp2 content. The nanomechanical measurements show that the filmdeposited at a helium partial pressure of 2.2 × 10−4 has the highest value of hardness (37.39 GPa) and elastic modulus (320.50 GPa). At a light intensity of 100 mW/cm2, the NCT filmsdeposited at 2.2 × 10−4 and 0.1 mbar partial pressures of helium gas exhibit good photoresponses of 2.2% and 3.6%, respectively.

X-ray excited Pu core–valence–valence and core–core–valence Auger line-shapes were used in combination with the Pu 4f photoelectron peaks to characterize differences in the oxidation state and local electronic structure for Pu compounds. The evolution of the Pu 4f core-level chemical shift as a function of sputtering depth profiling and hydrogen exposure at ambient temperature was quantified. The combination of the core–valence–valence Auger peak energies with the associated chemical shift of the Pu 4f photoelectron line defines the Auger parameter and results in a reliable method for definitively determining oxidation states independent of binding energy calibration. Results show that PuO2, Pu2O3, PuH2.7, and Pu have definitive Auger line-shapes. These data were used to produce a chemical state (Wagner) plot for select plutonium oxides. This Wagner plot allowed us to distinguish between the trivalent hydride and the trivalent oxide, which cannot be differentiated by the Pu 4f binding energy alone.

Cu(In,Ga,Al)Se2 (CIGAS) thin films were studied as an alternative absorber layer material to Cu(InxGa1−x)Se2. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350 °C, followed by postdeposition annealing at 520 °C for 5 h in vacuum. The film composition was measured by an electron probe microanalyzer while the elemental depth profiles were determined by secondary ion mass spectrometry.X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2θ values with increasing Al content. Scanning electron microscopy images revealed dense and well-defined grains, as well as sharp CIGAS/Si(100) interfaces for all films. Atomic force microscopy analysis indicated that the roughness of CIGAS films decreases with increasing Al content. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as Al content increased.